Designing sensors for pollutants has long been, and still is, an important technological challenge. U.S. Pat. No. 5,990,684, issued to Merrill (the '684 patent), which patent is herein incorporated by reference in its entirety, is directed to a “method and apparatus for continuously monitoring an aqueous flow to detect and quantify ions.” The method involves providing a conduit having at least one ion collection portion, disposing the aqueous flow through the conduit, attracting target ions to the ion collection portion such that they are bonded to the ion collection portion, and detecting a contaminant, or contaminants, based upon a predetermined property of the plurality of target ions bonded to the ion collection portion. In the preferred embodiment of the method, the predetermined property is a conductivity of the target ions, and the detecting step involves measuring a change in conductivity of the collection portion as ions are bonded and comparing that conductivity to a predetermined conductivity. The apparatus includes a conduit into which an ion collection portion is disposed, a sensor that senses ions collected on the ion collection portion and sends a signal corresponding to a value of a predetermined property of the ions, and a microprocessor in communication with the sensor and programmed to process the signal and determine the presence of the at least one contaminant based upon the processed signal.
A particularly useful molecular sensing technology is based on quartz crystal microbalances (QCMs), a family of very sensitive and inexpensive sensors that produce a frequency shift in quartz crystal vibration when molecules interact with the sensor surface. These sensors can be used in both the gas and liquid phases, and generate a signal that is generally proportional to the concentration of the interacting molecules. Gas phase QCMs are commercially used in the electronic industry.
In the liquid phase, QCMs have been coupled to antibodies, allowing for the selective sensing of the antibody conjugate. More recently, a technique called “molecular imprinting” has also been used. Molecular imprinting polymerization (MIP) is a molecular technology that allows for the selective recognition of targeted molecules by cross-linked polymers. This technique consists of coating a cross-linked templated polymeric layer to the QCM surface.
Though recent, the molecular imprinting technique is known in the art. For example, U.S. Pat. No. 5,630,978 discloses a method for preparing mimics of a wide variety of drugs and other biologically active molecules using molecular imprinting techniques. Additionally, U.S. Pat. No. 5,959,050 is directed to a molecularly imprinted support formed from at least two distinct acrylic monomers and at least one imprinted molecule. What is needed in the art, therefore, is the use of MIP techniques in QCM-based sensors for continuous on-line monitoring of harmful, water-borne organic contaminants.